1. Field of the Invention
The present invention relates to a propylene-based polymer and a method for production the same, along with a propylene-based resin composition with excellent impact resistance, and in more detail, relates to a propylene-based polymer having excellent mechanical properties such as impact resistance or tensile strength at break while maintaining high rigidity, and also having improved melt fluidity and excellent moldability and appearance, and a method for production the same, along with a propylene-based resin composition characterized by containing, as an impact modifier component, a propylene-ethylene copolymer component, which is constituted of a crystalline propylene polymer component and a propylene-ethylene random copolymer component, having the propylene-ethylene copolymer component, which is produced by a multi-stage polymerization method, as a main component, and containing a copolymer, where a part of the crystalline propylene polymer component and the propylene-ethylene random copolymer component, which are produced sequentially by a multi-stage polymerization, is chemically bonded. In addition, the present invention relates to a propylene-based polymer resin composition, which has remarkably improved impact resistance, containing further ethylene/α-olefin-based elastomer or styrene-based elastomer, and an inorganic filler, in addition to the above components.
2. Background of the Prior Art
Conventionally, polypropylene has been used widely in various fields, because of having features of high melting point, high tensile strength, high rigidity and chemical resistance. However, a homopolymer of propylene with a single composition alone has a defect of being brittle against deformation, and has a problem of insufficient property such as impact resistance or tensile elongation at break. In addition, usual polypropylene has a problem that melt tension and melt viscoelasticity are low, which limits applications to thermoforming, foaming, blow molding and the like. Still more, there is a defect that poor non-Newtonian property and small swell result in deteriorated appearance such as generation of flow-mark in a molded article.
As a method for improving the above impact resistance or tensile elongation at break of polypropylene, such a method has been used often that produces a block copolymer by blending a crystalline propylene-based polymer component and an elastomer component in a polymerization step.
This blended substance is generally called a propylene-based block copolymer, however, it is not, in the strict sense, a block copolymer, where the crystalline propylene-based polymer component and the elastomer component are chemically bonded. Therefore, the elastomer component results in coarse phase separation, in the crystalline propylene-based polymer component, and there has been limitation as a method for improving impact resistance or tensile elongation at break.
In view of such circumstance, it has been desired to be capable of producing a block copolymer, where the crystalline propylene-based polymer component and the elastomer component are truly bonded chemically, as a method for controlling a phase separated structure and improving impact resistance or tensile elongation at break.
As a method for producing such a block copolymer, it is thought of a method for copolymerizing a propylene-based macromer having a copolymerizable vinyl group at the terminal, and propylene or the like, however, when a catalyst for PP polymerization like a conventional Ziegler-Natta catalyst is used, a terminal structure results in a saturated alkyl terminal, which is mainly generated by chain transfer with hydrogen, and not a copolymerizable macromer. In addition, even a by-produced unsaturated alkyl terminal is generated as a not copolymerizable vinylidene terminal, therefore it was impossible to produce a block copolymer, where the crystalline propylene-based polymer component and the elastomer component are truly bonded chemically.
Incidentally, it has been known that a vinyl structure can be synthesized preferentially at a terminal, when a complex having a peculiar structure is used (for example, refer to Patent Literature 1, Non-Patent Literature 1, 3 and the like). And there has been disclosed a method for synthesizing a propylene-based macromer by using such a complex, and then copolymerizing with propylene (refer to Patent Literature 2, 3, Non-Patent Literature 2, 4 and the like).
However, compounds disclosed in Patent Literature 2 and Non-Patent Literature 4, although having a branched structure, because of not being constituted of the crystalline propylene-based polymer component and the elastomer component, do not show improved mechanical properties such as impact resistance. In addition, molecular weight of the side chain of the compound disclosed in Patent Literature 2 is, as Mn, 13,000 (about 25,000 as Mw) at the highest, and not sufficiently high, which provides only insufficient improvement effect of melt properties. In addition, modification effect to enhance mechanical properties is not sufficient.
In addition, compounds disclosed in Patent Literature 3 and Non-Patent Literature 2, because of using atactic polypropylene (atactic PP) as an amorphous moiety, result in denaturing a structure of the matrix itself, which the crystalline propylene-based polymer constitutes, and has a problem of deterioration of mechanical properties such as rigidity. In addition, molecular weight of the side chain of the compound disclosed in Patent Literature 3 is, as Mn, 15,700 (about 30,000 as Mw) at the highest, and not sufficient as molecular weight of the side chain, which provides only insufficient improvement effect of melt properties. In addition, modification effect to enhance mechanical properties is not sufficient.
In view of the above circumstance, there have been disclosed propylene-based copolymers having a structure having, as the side chain, an amorphous polymer with composition different from the crystalline propylene-based polymer as an amorphous moiety. For example, there have been disclosed propylene-based copolymers suitable as a compatibilizer of a propylene-based homopolymer and a propylene-based copolymer, specifically, propylene-based copolymers having an ethylene-propylene-based copolymer, as the side chain (refer to Patent Literature 4, 5).
However, these propylene-based copolymers, because of insufficient length of the branched chain, have insufficient effect to improve melt properties.
Still more, in order to improve these defects, there has been disclosed a compound obtained by copolymerizing a high molecular weight EPR macromer, and a production method (refer to Patent Literature 6 etc.), however, molecular weight of the side chain is, as Mn, 14,900 (about 25,200 as Mw) at the highest, and still not sufficient to attain high molecular weight, resulting in insufficient improvement effect of melt properties.
In addition, these methods require use of slurry polymerization at relatively high temperature and under low pressure, to efficiently generate a macromer having a vinyl structure at the terminal, which is not preferable in view of production efficiency and environmental load.
In addition, there have been disclosed the compounds obtained by copolymerization of α, ω-diene, in order to efficiently synthesize an EPR macromer and a PP macromer having a vinyl group at the terminal (refer to Patent Literature 7, 8 etc.).
However, when α, ω-diene is used, there is a problem that a cross-linking reaction is proceeded simultaneously with copolymerization, resulting in gel. In addition, residue of unreacted α, ω-diene in a copolymer produced by such a method raises a problem that odor is left even after converting the compounds to a composition or a molded article.
In view of the above problems, T. C. Chung et. al. have devised a polymerization method for branching isotactic PP, and a structure of the resulting branched compound (refer to Non-Patent Literature 5 etc.), however, this method requires use of a styrene derivative at a branch site, which raises a problem of amount of the branch sites or chemical stability of the branched sites. In addition, because the compound contains a benzene ring, it may generate a problem of also cleanness of the polymer.
Still more, there has been disclosed the grafting technology of isotactic PP on to diene moieties of ethylene-propylene-diene methylene rubber (hereafter referred to as EPDM) (refer to Patent Literature 9, Non-Patent Literature 6 etc.), however, molecular weight of the segment containing crystalline ethylene of the main chain is about 30,000, and not sufficient, which provides insufficient improvement effect of melt properties.
In addition, a polypropylene resin to be held an important position as an industrial material, is very excellent in rigidity or heat resistance or the like, however, because of having relatively low impact resistance, which is important as property, there has been known conventionally a method for enhancing impact resistance by making a propylene-ethylene random copolymer or a composition by blending polypropylene and a copolymer thereof.
Among them, such a composition obtained by a series of polymerization steps, that is, typically, one obtained by producing crystalline polypropylene in the first step, and a propylene-ethylene random copolymer in the second step, is usually called a propylene-ethylene block copolymer.
Such a propylene-ethylene block copolymer is industrially produced, usually, by using a Ziegler-Natta-based catalyst, however, it has been known that the Ziegler-Natta-based catalyst generally has a plurality kinds of active sites (so called multi-sites), and provides wide molecular weight distribution or wide comonomer composition distribution of a propylene-ethylene copolymer moiety. Thus, the propylene-ethylene block copolymer produced by using the Ziegler-Natta-based catalyst provides a molded article having relatively good rigidity-impact resistance balance, due to having wide composition distribution, and also having good moldability due to wide molecular weight distribution. Thus, because the propylene-ethylene block copolymer produced by using the Ziegler-Natta-based catalyst exerts excellent performance in balance of various properties, it has been utilized in many industrial fields starting from automotive interior and exterior parts or packaging materials.
However, in recent concerns to resource problems, energy problems and the like, request to a material for further thinning and light weight is continual, and expectation for a propylene-ethylene block copolymer, which is an impact resistant material, to enhance impact resistance performance has been increasing more and more.
Up to now, in order to enhance rigidity or heat resistance and impact resistance etc. of such a propylene-ethylene block copolymer in good balance, it has been considered necessary to maintain more sufficient impact resistance in a copolymer component and at the same time to control compatibility between crystalline polypropylene and a copolymer component within a proper range, and a method for enhancing the compatibility, by the addition of a compatibilizer component of a polypropylene component and a copolymer moiety, has been known conventionally (for example, refer to Patent Literature 10, 11).
In these methods, in recent years, there have been disclosed copolymers, which are said to be excellent also in impact resistance at low temperature, constituted of a crystalline polypropylene component, a copolymer component having relatively low ethylene content as a compatibilizer, and a copolymer component having relatively high ethylene content, by further specifying ultimate viscosity or MFR of the each component (for example, refer to Patent Literature 12, 13).
In addition, also in order to enhance balance between rigidity or heat resistance and impact resistance of the propylene-ethylene block copolymer, produced by using a metallocene catalyst (what is called a single-site catalyst), which has been used increasingly in recent years, there has been proposed a production trial, by at least three-stage polymerization, of a propylene-based resin composition excellent in balance between rigidity or heat resistance and impact resistance, which contains a compatibilizer component of a metallocene-based propylene-ethylene copolymer, similarly as in a method for using the above Ziegler-Natta-based catalyst (refer to Patent Literature 14).
Still more, the present inventors have proposed a method for enhancing rigidity and impact resistance, by the addition, as a modifier, of a propylene-ethylene block copolymer produced by a metallocene-based catalyst constituted of at least three components, containing a compatibilizer, to a propylene-ethylene block copolymer produced by the Ziegler-Natta-based catalyst (for example, JP-application No. 2006-34573).
Thus, as a method for enhancing impact resistance of the propylene-ethylene block copolymer produced by the Ziegler-Natta-based catalyst, in many cases, by noticing compatibility between the crystalline propylene component and the propylene-ethylene random copolymer, a method for enhancing impact resistance by modifying characteristics of interface thereof has been adopted in many cases, however, enhancing compatibility of a crystalline moiety and an amorphous moiety by modification of the interface results in decrease in modulus of rigidity, therefore it can be said that enhancement of rigidity-impact resistance balance is very difficult, and there is still left room to study.    Patent Literature 1: JP-A-2001-525461    Patent Literature 2: JP-A-2001-525460    Patent Literature 3: JP-A-2001-525463    Patent Literature 4: JP-A-10-338704    Patent Literature 5: WO 01/07493    Patent Literature 6: WO 02/079322    Patent Literature 7: JP-A-2004-35769    Patent Literature 8: JP-A-2004-143434    Patent Literature 9: EP No. 366411    Patent Literature 10: JP-A-57-67611    Patent Literature 11: JP-A-61-152442    Patent Literature 12: JP-A-2003-327642    Patent Literature 13: JP-A-9-48831    Patent Literature 14: WO 95/27741    Non-Patent Literature 1: RESCONI J. Am. Chem. Soc., 1992, 114, 1025    Non-Patent Literature 2: Shiono, T. Macromolecules, 1999, 32, 5723-5727    Non-Patent Literature 3: Macromol. Rapid Commun., 2000, 21, 1103    Non-Patent Literature 4: Macromol. Rapid Commun., 2001 22, 1488    Non-Patent Literature 5: Progress in polymer science 27 (2002), p 70 to 71    Non-Patent Literature 6: Macromolecules, 1991, 24, 561